Polysiloxane based emulsions have been employed in the prior art for rendering flexible sheet materials non-adherent to surfaces that would ordinarily adhere thereto. These products have normally consisted of a silanol chain-stopped di-substituted polysiloxane which is cross-linked with a hydrogen containing polysiloxane. This reaction has been catalyzed by an organotin salt of a fatty acid.
In copending application Ser. No. 419,372, filed Nov. 27, 1973 and now U.S. Pat. No. 3,900,617 the limitations of the above-noted systems have been mentioned. That application is hereby incorporated by reference.
It has now been discovered that a greatly improved product for rendering flexible sheet material non-adherent to surfaces that would ordinarily adhere thereto will be obtained from a vinyl containing polysiloxane based emulsion, if the vinyl containing polysiloxane is prepared using a different procedure. The novel process provides an emulsion product that offers the following advantages:
A. Lower manufacturing costs; PA1 B. Improved shear, dilution and freeze-thaw stability; PA1 C. Less penetration into porous substrates; PA1 D. More resistance to inhibition of cure on selected substrates; PA1 E. More resistance to rub-off from certain substrates. PA1 i. a compound of the formula (R.sub.2 SiO).sub.4 wherein R is a monovalent hydrocarbon free of unsaturation; PA1 ii. a compound of the formula (RR.sup.1 SiO).sub.4 wherein R is the same as hereinabove defined and R.sup.1 is a hydrocarbon radical having vinyl unsaturation; PA1 iii. a benzene sulfonic acid compound of the formula: ##STR2## wherein R.sup.2 is an alkyl group of from 6--18 carbon atoms; and iv. a platinum catalyst if desired; PA1 i. the polysiloxane containing vinyl unsaturation that is produced by the above-described process; PA1 ii. an organic hydrogen polysiloxane having the formula: EQU (R).sub.a (H).sub.b SiO.sub.4-a-b/2 (VI) PA1 iii. a platinum catalyst effective to cause copolymerization of (i) and (ii); and
The above-described advantages are secured by preparing a polysiloxane having a vinyl unsaturation by a process which is based on first homogenizing the tetramer reactants in water in the presence of a substituted benzene sulfonic acid, heating the tetramer reactants to polymerize the polysiloxane and adding an alkanolamine to terminate the polymerization reaction. A platinum catalyst may be dispersed with the tetramers prior to polymerization without risk of poisoning or deactivation. Alternatively, the platinum catalyst may be dispersed into the finished emulsion after addition of the alkanolamine, or at any subsequent time prior to the preparation of the coating bath.